What is the ruling on praying in a mosque that formerly contained a grave which was then removed, and which was built on the land of a graveyard? And what is the ruling on the prayers that were performed therein before the grave was removed?

If the grave is removed from the mosque, prayer therein is permissible, and it does not matter that it was built on land that was a graveyard, after removing what was in it, or ensuring the disintegration of its remains. A mosque and a grave do not coexist in Islam; rather, the incidental one of them is removed. So if the mosque was built over a grave, the mosque must be demolished. And if the deceased was buried in the mosque, the grave must be exhumed and the body removed.

If the graveyard has become ancient and worn out, such that the traces of the dead have perished, it is permissible to utilize the land and build upon it. However, if a person prays in a mosque containing a grave out of ignorance, there is no sin upon him, and he is not required to repeat the prayer.